The inventive subject matter relates to power systems and, more particularly, to island grid power supply systems and methods.
In power grids, the AC frequency is generally an important parameter. For example, devices attached to a grid often synchronize themselves to the grid frequency. Grid-connected devices, such as transformers, motors and the like, are typically designed to operate at or near the nominal grid frequency.
In island grid applications, generating assets, such as diesel or gas powered generators and turbines, may experience transient conditions that cause the frequency of the grid to vary significantly. These transient conditions may include, for example, large load changes and sudden changes in power source availability, such as a fuel-powered generator shutting down or a variation in supply from a generating asset such as a wind or solar generator. Such variations in line frequency may result in dropped loads or damaged equipment. Such problems may be particularly pronounced in systems that use engine/generator sets powered by natural gas or other lower energy density fuels.
Island grid generators are often sized with significant excess rated continuous power capacity in order to carry peak loads, respond to large transient load steps, and provide redundancy in support of mission-critical operations. They may operate at very high utilization rates, for example, 24 hours a day, 7 days a week, 365 days a year, but at relatively low real load factors, commonly between 15-50%, for extended periods of off-peak time. Furthermore, manufacturer warranty requirements may result in additional costs due to the use of self-imposed, manual load banks. This operating profile may result in lower fuel efficiency, excessive wear and tear on generators, and notable increases in particulate matter (PM) and hydrocarbon (HC) emissions due to the incomplete combustion of diesel or natural gas fuel.
Natural gas is becoming a more desirable fuel for power generation than diesel because of lower fuel cost and emissions. The potential drawbacks of natural gas engines include reduced step response capability and poor control performance with light loads.